Faculty Publications

Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736

Publications by NITK Faculty

Browse

Author: search.filters.author.Prabhu, K.N.Subject: search.filters.subject.Heat transfer

Search Results

Now showing 1 - 10 of 22
  • No Thumbnail Available
    Item
    Inverse modeling of heat transfer with application to solidification and quenching
    (2002) Prabhu, K.N.; Ashish, A.A.
    The inverse modeling of heat transfer involves the estimation of boundary conditions from the knowledge of thermal history inside a heat conducting body. Inverse analysis is extremely useful in modeling of contact heat transfer at interfaces of engineering surface during materials processing. In the present work, the one-dimensional transient heat conduction equation was inversely modeled in both cartesian as well as cylindrical coordinates. The model is capable of estimating heat flux transients, chill surface temperature, and total heat flow from the source to the sink for an input of thermal history inside the sink. The methodology was adopted to solve boundary heat transfer problems inversely during solidification and quenching. The response of the inverse solution to measured sensor data was studied by carrying out numerical experiments involving the use of varying grid size and time steps, future temperatures, and regularization techniques.
  • No Thumbnail Available
    Item
    Experimental models for assessment of interfacial heat transfer in dip soldering
    (2010) Nyamannavar, S.; Prabhu, K.N.
    The success of a numerical simulation for solder solidification during soldering processes depends on an accurate knowledge of heat transfer phenomenon at the solder/substrate interface. Two experimental setups were designed to study the interfacial heat transfer at solder/substrate interface. In the first method, a cylindrical probe of substrate material was dipped in liquid solder and solder was allowed to solidify around the metal probe. In the second method the test probe was dipped in the bulk solder liquid of sufficiently large quantity and allowed to attain the surrounding solder liquid temperature. Temperature at the center of the probe was measured using thermocouple. Heat flux transients at the surface of the probe were estimated by lumped heat capacitance method. SEM study at the solder/substrate interfacial region for experiments of solidifying solder around the test probe revealed the existence of a clear gap with aluminum substrate. A conforming contact was obtained with copper substrate. The nature of heat flux transients was found to be different in two experiments. © (2010) Trans Tech Publications.
  • No Thumbnail Available
    Item
    Assessment of heat transfer during solidification of Al-22% Si alloy by inverse analysis and surface roughness based predictive model
    (Springer India sanjiv.goswami@springer.co.in, 2012) Jayananda; Prabhu, K.N.
    Heat flux transients were estimated during unidirectional downward solidification of Al-22% Si alloy against copper, die steel and stainless steel chills. The chill instrumented with thermocouples was brought into contact with the liquid metal so as to avoid the effect of convection associated with the pouring of liquid metal. Heat flux transients were estimated by solving the inverse heat conduction problem. Higher thermal conductivity of chill material resulted in increased peak heat flux at the metal/ chill interface. Peak heat flux decreased when 100 lm thick alumina coating was applied on the chill surface. The lower thermal conductivity of alumina based coating and the presence of additional thermal resistance decreases the interfacial heat transfer. For uncoated chills, the ratio of the surface roughness (R a) of the casting to chill decreased from 6.5 to 0.5 with decrease in the thermal conductivity of the chill material. However when coating was applied on the chill, the surface roughness ratio was nearly constant at about 0.2 for all chill materials. The measured roughness data was used in a sum surface roughness model to estimate the heat transfer coefficient. The results of the model are in reasonable agreement with experimentally determined heat-transfer coefficients for coated chills.
  • No Thumbnail Available
    Item
    Replacement of heat sink fan by nanocoolants for enhancement of CPU efficiency
    (Institution of Engineering and Technology journals@theiet.org, 2013) Siddique, A.B.; Prabhu, K.N.
    The highest temperature under which a CPU can operate without interruption is 90°C. Heat sink fans generally provided for removal of heat produced by the processor are proved to be inadequate when CPU usage is 100%. The objective of this work is to exploit the enhanced thermal properties of nanofluid for dissipation of heat from the Intel (R) Core (TM) i5- 2310 CPU @ 2.9GHz quad-core processor for cooling it to a suitable operating temperature. Nanocoolants were prepared with two types of nanoparticles, titania and copper. The volume percentage of nanoparticles in nanocoolants were 0.01 and 0.1. It was observed that nanofluids are more efficient coolants than the base fluid and found to be significantly better than the traditional heat sink fan, as indicated by the CPU temperature, under the same loading condition. The average CPU temperatures were 90°C, 58°C, 56.6°C and 54.5°C with heat sink fan, deionized water, 0.1 vol% TiO2 and 0.1 vol% Cu nanofluids respectively at the flow rate of 700ml/min and CPU usage of 100%. The lowest CPU operating temperature (54.5°C) was obtained with 0.1 vol% Cu at the flow rate of 700ml/min. The cooling of CPU was also affected by the flow rate and the volume fraction of nanoparticles in the nanocoolant.
  • No Thumbnail Available
    Item
    Thermal Resistance at the Polymer/Mold Interface in Injection Molding
    (Springer, 2022) Kamala Nathan, D.K.; Prabhu, K.N.
    In injection molding, the thermomechanical condition of the solidifying part inside the cavity determines the morphology developed during cooling and thus the final properties of the component. This condition is significantly affected by the thermal contact resistance (TCR) at the polymer/mold interface. TCR is one of the most significant heat transfer characteristics that affect the quality of injection-molded components. TCR values significantly influence the simulated temperature distribution of the solidifying part inside the cavity. Using incorrect TCR values affect the accuracy of the simulated results leading to defects in the molded components. Further, the overall heat transfer during injection molding is influenced by the coolant characteristics and the thermophysical properties of the mold material. This paper gives an insight into the role of thermal transport phenomenon in the injection molding process, and particularly the importance of TCR during simulation of injection molding. © 2021, The Indian Institute of Metals - IIM.
  • No Thumbnail Available
    Item
    Heat transfer and solidification behaviour of modified A357 alloy
    (2007) Kumar, G.; Hegde, S.; Prabhu, K.N.
    Al-Si alloys are subjected to melt treatment like modification to improve their mechanical properties. Non-destructive technique like thermal analysis is generally used to assess the effectiveness of melt treatment. In the present study, the behaviour of the melt treated Al-7Si-Mg alloy (A357) during solidification with or without chilling was investigated using thermal analysis. Thermal analysis and heat transfer parameters were determined. Thermal analysis parameters were affected significantly by modification and chilling. Modification treatment resulted in the increase of cooling rate, heat evolved, casting/mould interfacial heat flux and eutectic growth velocity. A theoretical model based on undercooling from the equilibrium temperature during eutectic solidification was used to predict growth velocities and eutectic grain size. The eutectic grain sizes estimated using the model and those measured from casting microstructures were found to be in good agreement. © 2006 Elsevier B.V. All rights reserved.
  • No Thumbnail Available
    Item
    Effect of section size and agitation on heat transfer during quenching of AISI 1040 steel
    (2007) Fernandes, P.; Prabhu, K.N.
    In the present work an attempt has been made to determine the heat flux transients during quenching of Ø28 mm × 56 mm height and Ø44 mm × 88 mm height AISI 1040 steel specimens during lateral quenching in brine, water, palm oil and mineral oil. The heat flux transients were estimated by inverse modeling of heat conduction. The variation of heat flux transients with surface temperature for different quenching media is investigated. Higher peak heat flux transients are obtained for 28 mm diameter specimen than 44 mm diameter specimen during quenching in aqueous media. However quenching with oil media shows opposite results. Agitation of quenching medium increases the peak heat flux during the quenching of steel specimen in all the quenching media. Peak hardness is obtained at the surface and with smaller diameter specimens during agitation. © 2006 Elsevier B.V. All rights reserved.
  • No Thumbnail Available
    Item
    Nanoquenchants for industrial heat treatment
    (2008) Prabhu, K.N.; Fernades, P.
    The present work outlines the possibility of using nanofluids for industrial heat treatment. Development of nanoquenchants having (i) high quench severity for enhancement of heat transfer for thick sections with low quench sensitivity and (ii) low cooling severity for thin sections with high quench sensitivity would be extremely useful to the heat treating community. The temperature dependent heat transfer coefficient and the wettability of the medium are the two important parameters that can be used to characterize a nanoquenchant to assess its suitability for industrial heat treatment. © 2007 ASM International.
  • No Thumbnail Available
    Item
    Comparative study of heat transfer and wetting behaviour of conventional and bioquenchants for industrial heat treatment
    (2008) Fernandes, P.; Prabhu, K.N.
    An investigation was conducted to study the suitability of vegetable oils as bioquenchants for industrial heat treatment. The study involved the assessment of the severity of quenching and wetting behaviour of conventional and vegetable oil quench media. Quench severities of sunflower, coconut and palm oils were found to be greater than mineral oil. The quench severity of aqueous media is greater than oil media although their wettability is poor as indicated by their higher contact angles. A dimensionless contact angle parameter defined in this work is found to be a better parameter to compare the wetting behaviour with heat transfer. © 2007 Elsevier Ltd. All rights reserved.
  • No Thumbnail Available
    Item
    Thermal contact at solder/substrate interfaces during solidification
    (2009) Nyamannavar, S.; Prabhu, K.N.
    Heat flux transients at the solder/substrate interface during the solidification of Sn-37Pb and Sn-3.5Ag solder alloys against metallic substrates were estimated by the lumped heat capacitance model and the contact condition was assessed by scanning electronic microscopy (SEM). Copper substrates yielded maximum contact heat flux followed by brass and aluminium substrates. The SEM study in the solder/substrate interfacial region revealed the existence of a clear gap with the aluminium substrate. A conforming contact was obtained with copper and brass substrates. © 2009 Institute of Materials, Minerals and Mining.